Fully dense consolidated-powder superalloys

ABSTRACT

Superalloys formed of consolidated powder, which are fully dense and have a composition by weight consisting essentially of about 0.70 to 1.2 percent carbon, about 18 to 24 percent chromium, about 7 to 12 percent tungsten, about 3 to 11 percent tantalum, about 0.05 to 2.5 percent zirconium, and the balance cobalt together with minor alloying ingredients and incidental impurities, are characterized by being readily workable as compared to conventional casting alloys of the same chemical composition which are too brittle and have too little ductility to hot work.

United States Patent Fletcher 1 Mar. 14, 1972 [54] FULLY DENSE CONSOLIDATED- POWDER SUPERALLOYS [72] Inventor: Stewart G. Fletcher, Latrobe, Pa.

[73] Assignee: Latrobe Steel Company, Latrobe, Pa.

[22] Filed: Feb. 16, 1970 [2]] Appl. No.: 11,859

[52] US. Cl. ..75/171, 29/182, 75/0.5 BB, 75/0.5 C [51] Int. Cl ..C22c 19/00 [58] Field ofSearch ..75/l7l, 170, 0.5 BB, 0.5 C; 148/32, 32.5; 29/182 [56] References Cited UNITED STATES PATENTS 5 2 1,744 8/1970 Parikh ..75/ 17 l I Examiner-Richard 0. Dean AttorneyFidler, Bradley, Patnaude & Lazo ABSTRACT Superalloys formed of consolidated powder, which are fully dense and have a composition by weight consisting essentially of about 0.70 to 1.2 percent carbon, about 18 to 24 percent chromium, about 7 to 12 percent tungsten, about 3 to 11 percent tantalum, about 0.05 to 2.5 percent zirconium, and the balance cobalt together with minor alloying ingredients and incidental impurities, are characterized by being readily workable as compared to conventional casting alloys of the same chemical composition which are too brittle and have too little ductility to hot work.

6 Claims, No Drawings FULLY DENSE CONSOLIDATED-POWDER SUPERALLOYS The present invention relates to a workable high-temperature superalloy" and more particularly to a heat-resistant, high-strength, structural alloy of fully dense consolidated powder prepared from solidified powder particles featuring an ultrafrne microstructure in which the secondary dendrite arm spacing is substantially all less than about 0.0003 inch and in which the microsegregation of the consolidated alloy has been reduced to limits heretofore unattainable.

The utilization of high temperatures for many diverse operations has become an accepted part of the technology of modern industrial processes. Also, the quest for improved power sources has led to the development of such devices as superchargers, gas turbines, jet engines and the like all operating at elevated temperatures. These developments demand metals and alloys which will withstand prolonged exposure to temperatures well above about 1,300 F. and in many instances well above about 1,700 F., and are capable of withstanding severe mechanical stress at these temperatures. In many instances it is desired that alloys for use in such apparatus be capable of being hot-worked and machined, while in other instances the alloys may be employed in the form of castings. In any event such alloys must have high strength in order to be useful.

At the present time a number of relatively highly alloyed cobalt base alloys, commonly referred to in the trade as superalloys, are commercially available. One such alloy commonly referred to as Mar-M-322 has the following composition: about 1.0 percent carbon, about 21.5 percent chromium, about 9 percent tungsten, about 4.5 percent tantalum, about 2.0 percent zirconium, about 0.75 percent titanium and the balance cobalt with usual impurities in ordinary amounts. A similar commercial alloy known as Mar-M-302 has the following composition: about 0.85 percent carbon, about 21.5 percent chromium, about 10 percent tungsten, about 9 percent tantalum, about 0.2 percent zirconium, about 0.005 percent boron and the balance cobalt with usual impurities. Commercial alloys such as Mar-M-322 and Mar-M-302 have good oxidation resistance and retain fairly good strength values up to temperatures of 1,800" F. or even in some cases up to 2,000 F. These cobalt base alloys are casting alloys which have relatively low ductility and accordingly are used in their as-cast shape.

Presently as-cast cobalt base alloys which correspond compositionally to the alloys in the novel form of the present invention are characterized by relatively coarse dendritic structure which seriously detract from the physical and metallurgical properties of the materials. Because of this undesirable microstructure these alloys are brittle and extremely difficult to fabricate into useful shapes.

The present invention provides cobalt base alloys in a novel form which overcome numerous shortcomings and disadvantages of previously known alloys and which have particular utility at high temperatures. Such alloys are considerably stronger than presently available cast alloys of similar chemical composition, but at the same time are readily fabricable into useful wrought forms.

Alloys of the present invention can have the general composition range of:

Percent by Weight C Above 0.70 to 1.2 Cr About 18 to 24 W About 7 to 12 Ta About 3 to l l Zr About 0.05 to 2.5 Si Les than 0.40 Mn Less than 0.20

Fe Less than 1.5

Ti Less than 0.9

8 Less than 0.01

Balance substantially cobalt with residual impurities in ordinary amounts.

Preferred compositions for most applications in accordance with the present invention have the composition range of:

Percent by Weight I II C 0.9-1.1 0.70-0.93 Cr 20-23 20-23 W 8-10 9-11 Ta 4-5 8-10 Zr 2-2.5 0.1-0.3

Si. max. 0.20 0.40 Mn. max. 0.20 0.20 Fe, max. 1.5 1.5

8, max. 0.01

Balance substantially cobalt with residual impurities in ordinary amounts.

The expression less than followed by a percentage Figure for silicon, manganese, iron, titanium and boron means that the particular element may be entirely absent or may be present up to the concentration given without deleteriously affecting the alloy.

Each of the superalloys provided by the present invention, through compositionally similar to certain alloys of the prior art, can be distinguished therefrom by its novel metallographic structure with the attendant increase in desirable mechanical properties. More specifically, each of the present cobalt-base alloys is characterized by being readily workable.

Because of the high ductility of the unique ultrafine microstructure, the cobalt base alloys of this invention can be readily fabricated into useful shapes and retain a large amount of the cold work induced during fabrication which improves the strength of the alloys.

In accordance with the present invention an atomized, prealloyed powder of the desired composition is first made by atomizing a molten alloy charge consisting essentially of the ingredients in substantially the proportions stated in the general compositions set out hereinabove. The molten alloy charge can be obtained if desired, by melting conventional casting alloys such as are disclosed in U.S. Pat. No. 2,974,036, patented Mar. 7, 1961, and U.S. Pat. No. 3,333,957, patented Aug. 1, 1967, the disclosures of each of said patent being incorporated herein by reference. Accordingly, the alloys produced in accordance with the invention include a fully dense consolidated-powder alloy having the composition defined by any of claims 1-7 of U.S. Pat. No. 2,974,036 or any of the claims l-7 of U.S. Pat. No. 3,333,957, wherein the improvement comprises the hot workability of the alloy. The atomized alloy charge is then rapidly quenched to solidify the molten particles and prevent appreciable formation of coarse crystals of dispersed secondary phase in the resultant powder. The prealloyed powder is then compressed and mechanically hot worked to consolidate the powder into metal stock having a density substantially equivalent to the alloy in its cast state.

Cobalt-base alloys with the composition set out in Table l were made according to this invention and compared with a prior art alloy of nearly identical chemical composition.

1 Maximum. 1 Balance.

Alloys to be atomized were heated to a temperature of about 200 to 300 F. above fusion temperature in an induction-heated magnesia crucible under an argon blanket. The

molten metal in 5 lb. lots was poured into a preheated zirponia-lined tundish which had a 3/ 16-inch opening in the bottom. The narrow stream of the molten alloy charge from the tundish passed through the center of a mild steel. zirconia lined nozzle of %-inch-diameter opening and was atomized by a jet of high-pressure (350 psi.) argon ust below the tip of the nozzle. The droplets of prealloyed atomized alloy were rapidly quenched by the inert gas and by a large reservoir of water in the bottom of the atomizing chamber.

The atomized powder obtained was washed several times with acetone. dried and screened to 60 and 60 mesh size fractions. The 60 mesh portion was placed in an lnconel 600 pipe for consolidation. The can was lined with a sheet of molybdenum to prevent bonding between the can and the powder during consolidation and to facilitate removal of the can material after fabrication. The powders were packed into the can on a vibrating table to obtain as much settling as possible and then cold pressed at 20 t.s.i. After the lids were welded pn, the cans were hammer forged from approximately 2 inches down to a billet approximately 0.5 inch in height at a temperature of from 2,100 to 2.150 F. Following reheating the resultant billet was hot rolled at the same temperature to a final thickness of 0.200 inch. a total reduction of 90 percent. using a l0 percent reduction in thickness for each rolling pass. The consolidated material was then air cooled to room temperature. the plates were annealed. the canning material stripped away and the wrought material sectioned for testing.

lMetallographic observations were made on each batch of atomized powder and on each consolidated and annealed plate. Photomicrographs were taken at l000X so that microstructural comparisons could be made between commercially produced and atomized and consolidated alloys. Tensile specimens were taken from the centermost portion of the forged and rolled plate which represented the area of densest material. Room temperature and elevated temperature tensile tests at temperatures from 1.400 to 2.000 F. were performed in a vacuum of better than lX torr at a strain rate of 0.05 inch per minute. Material for the test specimens was machined mto sheet tensile specimens approximately 2 inches long (1 inch gauge section). 0.050 inch thick, and 0.5 inch wide (0.20 inch in gauge section). The specimens were tested in the asrolled condition without heat treatment. Ultimate tensile strength. 0.2 percent ofiset yield strength and percent elongation in a 1.0 inch gauge length. were determined from loadelongation curves and from measurements of the gauge length tcribe marks on the broken tensile specimens. The results of these tests appear in Table ll.

perature the tensile and 0.2 percent yield strengths of the atomized and consolidated alloy of the present invention are appreciably greater than the tensile and 0.2 percent yield strengths of cast alloys produced in the conventional manner. Metallographic observations showed that dendrite spacing of these atomized superalloys is significantly refined in comparison to conventionally melted and cast superalloys. For example alloys EL 89 and EL 88 showed a secondary dentrite arm spacing of 0.00008 and 0.00006 inch. respectively. in pomparison to the conventional melted and cast alloys such as Mar-M-22 and Mar-M-302 having a dentrite arm spacing of 0.005 and above.

The elevated temperature tensile properties of the atomized and consolidated cobalt-base alloys of the present invention were found to be superior to those of the corresponding commercial products (not workable) at l,400 F. These tensile properties are given in Table [11. Tests were carried out at a 0.005 inch per min. rate through the 0.2 percent offset yield point and than at 0.050 inch per min. to failure.

TABLE ill Alloy lEL-88 Mar-M402 Heat Treatment llS rolled Hardness lRc 48.3 Test Temperature ll400 F. L400 F. Tensile Strength (p.s.i.) ll63.000 80.000 0.2 Yield Strength (p.s.|.) 107.000 50.000 Elongation (5) 7 l \lloy EL-89 Mar-M422 Heat Treatment as rolled t90b) Hardness Rc 52.3 Test Temperature l .400 F. L400 F. Tensile Strength (p.s.i.) 178.000 l00.000 0.2% Yield Strength (p.s.|.) ll l6.000 55.000

Elongation (Ki) 6 B What is claimed is:

l. A fully dense consolidated-powder alloy consisting essentially of:

carbon about 0.70 to L2 percent chromium about 18 to 24 percent tungsten about 7 to 12 percent tantalum about 3 to l l percent .mrconium about 0.05 to 2.5 percent silicon about 0 to 0.40 percent manganese about 0 to 0.20 percent iron about 0 to l .5 percent titanium about 0 to 0.9 percent boron about 0 to 0.01 percent and the balance cobalt with usual impurities in ordinary amounts. said alloy being characterized by being hot workable.

.2. An alloy having the composition of the alloy of claim 1, prepared by consolidation of a powder in which the dendrite arm spacing is less than about 0.0003 inch.

3. An alloy according to claim 1. consisting essentially of:

carbon about 0.9 to L1 percent chromium about 20 to 23 percent tungsten about 8 to l0 percent tantalum about 4 to 5 percent tirconium about 2 to 2.5 percent titanium about 0.65 to 0.85 percent tilicon about 0.20 percent maximum manganese about 0.20 percent maximum ll'Oll about l.5 percent maximum and the balance cobalt with usual impurities in ordinary amounts.

l. A fully dense consolidated-powder alloy consisting essentially of:

carbon about 1.0 percent chromium about 21.5 percent tungsten about 9 percent tantalum about 4.5 percent urconium about 2.0 percent titanium about 0.75 percent and the balance cobalt with usual impurities in ordinary amounts. said alloy being characterized by being hot workable.

.5. An alloy according to claim 1. consisting essentially of:

carbon about 0.78 to 0.93 percent chromium about 20 to 23 percent tungsten about 9 to l 1 percent tantalum about 8 to 10 percent .nrconium about 0.1 to 0.3 percent silicon about 0.4 percent maximum tungsten about 10 percent tantalum about 9 percent zirconium about 0.2 percent boron about 0.005 percent and the balance cobalt with usual impurities in ordinary amounts, said alloy being characterized by being hot workable.

# #8 I t it UNITED STATES PATENT OFFICE CERTIFICATE @F QGRRECTIGN Patent No. 3 6L .9 256 Dated March 14 1972 Inventor S G It is certified that error appearsvin the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 37, "better than 1X should read --better than lXl0 Table II, line f fi "1000,000" should read --lO0,000--. Column 4', line l, "Mar-M- -ZZ" should read -MarM-322- Signed and sealed this 29th day of August 1972.

(SEAL) Atte st 2 EDWARD I LFLETCHER, JR

"'Ip 1X Attesting Officer ROBER COTTbLHALK Commissioner of Patents F ORM PO-105O (IO-69) USCOMM-DC 60376-1 69 a U5. GOVERNMENT PRINTING OFFICE: 1959 0*356-334 UNITED STATES PATENT OFFICE CERTIFICATE 6F CORRECTION Patent No. 3 ,649,256 Dated March 14; 1972 l STEWART G. FLETCHER It is certified that error appearsin the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 37, "better than 1x should read --better than 1X10 Table II, line 5*? "1000,000" should read --lO0,000-. Column 4', line 1, '.'Mar-M22" should read -Mar-M-322 Signed and sealed this 29th day of August 1972.

(SEAL) Attest 2 EDI- IARQDLFLETCHMR,JR. ROBERT GOTTSCHALK Attestlng Offlcer Commissioner of Patents F ORM PO-lOSO (10-69) USCOMM-DC 50376-P69 9 U.5, GOVERNMENT PRINTING OFFICE: 1959 O-35G-334 

2. An alloy having the composition of the alloy of claim 1, prepared by consolidation of a powder in which the dendrite arm spacing is less than about 0.0003 inch.
 3. An alloy according to claim 1, consisting essentially of: carbon about 0.9 to 1.1 percent chromium about 20 to 23 percent tungsten about 8 to 10 percent tantalum about 4 to 5 percent zirconiUm about 2 to 2.5 percent titanium about 0.65 to 0.85 percent silicon about 0.20 percent maximum manganese about 0.20 percent maximum iron about 1.5 percent maximum and the balance cobalt with usual impurities in ordinary amounts.
 4. A fully dense consolidated-powder alloy consisting essentially of: carbon about 1.0 percent chromium about 21.5 percent tungsten about 9 percent tantalum about 4.5 percent zirconium about 2.0 percent titanium about 0.75 percent and the balance cobalt with usual impurities in ordinary amounts, said alloy being characterized by being hot workable.
 5. An alloy according to claim 1, consisting essentially of: carbon about 0.78 to 0.93 percent chromium about 20 to 23 percent tungsten about 9 to 11 percent tantalum about 8 to 10 percent zirconium about 0.1 to 0.3 percent silicon about 0.4 percent maximum manganese about 0.2 percent maximum iron about 1.5 percent maximum boron about 0.01 percent maximum and the balance cobalt with usual impurities in ordinary amounts.
 6. A fully dense consolidated-powder alloy, consisting essentially of: carbon about 0.85 percent chromium about 21.5 percent tungsten about 10 percent tantalum about 9 percent zirconium about 0.2 percent boron about 0.005 percent and the balance cobalt with usual impurities in ordinary amounts, said alloy being characterized by being hot workable. 